This is a proposal to study specific aspects of prenatal pituitary gland development. Our long-range goal is to determine the role that tissue interactions have in establishing lobe-specific biochemical differences between adult anterior and intermediate lobes of the pituitary gland. We will study differentiation of the two populations of proopiomelanocortin (POMC)-containing cells that are present in the anterior and intermediate lobes of the pituitary gland. Although POMC cells in both lobes make a similar precursor protein molecule, the precursor is processed in the adult animal to different lobe-specific end-product hormones. We will determine when and how during development these lobe-specific processing patterns are established. At the genetic level, we will use recombinant DNA probes to determine when POMC gene expression can first be detected and compare this to the time at which POMC-related peptides are first detected immunologically. We will also use these probes to localize POMC-producing cells in embryonic pituitary tissue sections at different times of development and establish techniques to examine the possible dual production of peptide hormone mRNAs in single cells during development. We will determine whether other proteins which exhibit lobe-specific localization in the adult pituitary are early markers of lobe-specific differentiation. We have determined that monoamine oxidase B distribution in the adult rat pituitary is lobe-specific and will extend this analysis to early fetal stages. Finally, we will begin to characterize the extracellular matrix (ECM) in the region of the developing pituitary and determine the role of ECM in establishing lobe-specific differentiation by in vitro culture studies.